Generally, in an element to be soldered such as a contact used in a connector, a foundation plating layer of nickel (Ni) is carried out on a metal material such as copper, and a gold plating is further carried out thereon. Owing to carrying out the gold plating on a surface of an element, not only the oxidization of the surface of the element can be prevented, but also a terminal of the element and a wiring pattern on a printed circuit board can easily be soldered owing to high wetting property between gold and solder.
On the other hand, a minute connector used in a mobile equipment such as a mobile phone or a digital still camera has a stacking height of the connector itself is about 1 mm when a socket and a header are coupled. Furthermore, a pitch of an arrangement of the contacts is about 0.4 mm and a height of the contact is about 0.7 mm. Thus, melted solder diffuses along a surface of the contact from the terminal portion due to the high wetting property between gold and solder, so that there is a possibility that the solder adheres at a portion such as a contacting portion to which the solder should not be adhered. Furthermore, there is a possibility that a sufficient connecting strength is not obtained due to deficiency of quantity of the solder adhered in the vicinity of the terminal portion and the wiring pattern on the printed circuit board which are to be soldered, according to the diffusion of the solder.
Therefore, as described in the publication gazettes of Japanese Patent Application 2-15662 and 6-204377, it is proposed to carry out partial plating for carrying gold plating only at the terminal portion and the contacting portion of the contact, surfaces of which are necessary to be plated with gold, so as not to be plated by gold at a portion between the terminal portion and the contacting portion. In this manner, when the foundation layer of nickel plating is unsheathed at the portion between the terminal portion and the contacting portion without plating gold, it is possible to prevent the diffusion of the solder from the terminal portion to the contacting portion due to low wetting property between nickel and solder.
The contact of the connector for mobile equipment, however, is much smaller, so that it is difficult to form the contact one by one and to carry out the plate on the contact entirely. Therefore, a side of a band metal plate is shaped like teeth of a comb, and the teeth portion is bend to have a predetermined shape, so that a semi-finished blank in which a lot of contacts are arranged at a predetermined pitch is formed. The semi-finished blank is dipped in a plating solution while it is conveyed in a lengthwise direction thereof, so that the nickel plating and the gold plating are carried out on entire surfaces of the contacts. Accordingly, it is very difficult to carry out the partial plating on the contacts. Even when the partial plating is forcibly carried out on the contacts, the processes and the plating machine for gold plating become very complex, and the conveying speed of the semi-finished blank becomes much slower, so that the productivity will be dropped.